With the growing interest in energy conservation, increasingly more industrial work machines are supplied with electric drive assemblies for driving the work machine and operating its various tools or functions. Ongoing developments in electric drives have made it possible for electrically driven work machines to effectively match or surpass the performance of purely mechanically driven work machines while requiring significantly less fuel and overall energy. As electric drive assemblies become increasingly more commonplace with respect to industrial work machines, and the like, the demands for more efficient generators and techniques for controlling same have also increased.
A generator of an electric drive machine is typically used to convert mechanical power received from a primary power source, such as a combustion engine, into electrical power for performing one or more operations of the work machine. Additionally, a generator may be used to convert electrical power stored within a common bus or storage device into mechanical power. Among the various types of generators available for use with an electric drive assembly, switched reluctance (SR) machines have received great interest for being robust, cost-effective, and overall, more efficient. While currently existing systems and methods for controlling SR machines provide adequate control, there is still room for improvement.
In particular, a switched reluctance machine with a power dense design may typically experience a sudden jump in power level during a continuous conduction mode. Moreover, when in continuous conduction, small changes to the control input of the switched reluctance machine may lead to significantly large changes in power. Accordingly, there is a need to provide a control system and method that minimizes power jumps in switched reluctance machines during continuous conduction.
A method of controlling a switched reluctance drive is disclosed in U.S. Pat. No. 6,972,533, entitled, “Control of a Switched Reluctance Drive.” The '533 patent describes a method of control that uses a combination of a switch-on angle, switch-off angle and current level to trigger an optional period of freewheeling which controls the standing current in the phase. In operation, the phase is switched on at the switch-on angle, and the current level is chosen a little below the natural peak current of the phase. The control system of the '533 patent is arranged such that when the phase current reaches the standing current, the phase is put into freewheel until the switch-off angle is reached.
While the '533 patent controls the standing current based on the current level, the '533 control system still uses the conventional on- and off-angles in addition to the standing current during continuous conduction. Using the conventional on- and off-angles may lead to unstable control of the switched reluctance drive because a small change in either of the angle parameters may lead to significant changes in power. Accordingly, improved systems and methods for controlling SR machines during continuous conduction are still needed.